The present invention relates to adhesive laminates having pressure-sensitive adhesives and a protective backing removably adhered to the adhesive, more particularly to such laminates having scored backings which can be easily removed from the laminate.
Adhesive laminates having removable backings that have been modified in a variety of ways to facilitate removal of the backings have been described. U.S. Pat. No. 3,230,649 to Karn describes adhesive laminates, such as label stock, in which the backing has a plurality of cuts so arranged that when a label of a certain minimum size is cut from the stock, at least one cut or portion of a cut will be found on the backing of the label. Both curved and straight cuts are shown, as well as cuts which extend only part of the way through the thickness of the backing sheet. Although such cuts offered a convenient starting point for removing the backing, it would often be necessary to remove the backing in more than two pieces, because the backing would tear between the cuts. The arrangement of aligned cuts spaced to provide a backing that ruptures when flexed is not described.
U.S. Pat. No. 3,006,793 to Wheeler describes adhesive laminates having backing sheets that can be removed in two pieces, at most, regardless of the size of the sheet being removed. The backing sheet has a number of embrittled zones or lines which are formed by applying an acid, such as sulfuric acid, or by using heat or ultraviolet radiation to embrittle narrow strips of the backing. When the laminate is bent sharply away from the backing side along a line of embrittlement, the backing cracks along the line, forming two continuous pieces of backing. The backing sheet has sufficient tensile strength in the embrittled zones so that it does not normally crack in the zones, unless deliberately bent more than is necessary to separate the backing from the rest of the laminate. Thus, the backing of a particular label containing many lines of embrittlement may be cracked selectively along one line of embrittlement and then removed in two continuous pieces. The ability of such a backing to be removed in two continuous pieces, at most, which is referred to herein as "pull-across", is highly desirable, particularly in large labels including many lines of embrittlement.
U.S. Pat. No. 4,264,662 to Taylor is an improvement to the '793 patent in the use of a polymer to seal zones of embrittlement.
U.S. Pat. No. 3,859,157 to Morgan describes adhesive laminates having backing sheets in which weakened areas or score lines are formed by mechanical crushing of the fibers of the backing. When the laminate is flexed away from the backing side, the backing ruptures at the score line, offering an easy starting point for removal of the backing. The score lines are made continuous or discontinuous to leave sufficient strength in the backing sheet, whereby it can be readily further-processed or prepared for use without any danger of splitting or tearing. Such a backing could not readily be removed in two pieces, at most, because the discontinuities in the score lines are said to be on the order of from 1/4 to 1/2-inch long and spaced at intervals of from 1 to 4 inches. Such discontinuities would prevent the backing from cracking clearly, and the backing would tend to tear irregularly between score lines.
U.S. Pat. No. 3,909,582 to Bowen, incorporated herein by reference, describes a method for forming a line of weakness, such as a tear line in a laminate, with the use of a laser. Described laminates may include layers of adhesive and of paper. The use of a pulsed carbon-dioxide laser and the selective scoring of a paper layer of a laminate are also described. However, the patent does not describe adhesive laminates having pressure-sensitive adhesives and backing sheets that can be cracked by bending the laminate and removed in two pieces, at most.
U.S. Pat. No. 3,419,706 to Lorhman, incorporated herein by reference, describes the use of a laser to cut paper. Pressure-sensitive-adhesive laminates having laser-scored backings are not described.